The control of fluid flow through flexible tubing is required in many technical fields of endeavor, including routine laboratory practices, and the chemical, biotechnological and medical fields. The present invention relates to an apparatus for clamping flexible tubes in a controlled manner so as to occlude the tube and thereby prevent the flow of fluid through the tube. The disclosed apparatus was developed in response to the need for an improved clamping apparatus for use in single needle hemodialysis, but will find widespread utility in many other applications.
Hemodialysis machines serve as artificial kidneys for extracting waste material from the blood of a patient whose kidneys do not function properly. Generally, this waste is removed from the patient's blood by dialysis through semipermeable barriers into a dialysate. This dialysis is performed in a hemodialysis machine. It is therefore required that blood be removed from the patient, conveyed to the hemodialysis machine for treatment and then returned to the patient. This is achieved by means of flexible tubes and a pump mechanism, such as a peristaltic pump.
In one type of hemodialysis, termed single needle hemodialysis, a single venipuncture needle is inserted into a vein in the patient's arm. This needle is used both to remove untreated blood from the patient and deliver it to the hemodialysis machine and to return treated blood to the patient from the hemodialysis machine. This blood removal and return is performed through two separate flexible tubes, both of which are operably attached to the single needle.
To avoid co-mingling of the treated and untreated blood, the dialysis machine operates on a dual phase cycle: in one phase, termed the arterial phase, blood is withdrawn from the patient through the needle and passed through one of the tubes, termed the arterial line, into the dialysis machine for treatment. During this arterial phase, the other tube, termed the venous line, is occluded. In the other phase, termed the venous phase, treated blood is pumped from the dialysis machine through the venous line, and returned to the patient through the needle, while the arterial line is occluded. The operation of a typical single needle hemodialysis apparatus is disclosed in U.S. Pat. No. 4,643,714. The pumping action required to convey the blood to and from the patient is typically performed by a peristaltic pump, such as is disclosed in U.S. Pat. No. 4,190,536.
The arterial and venous lines are typically made of flexible tubing. Clamps are used to occlude the arterial or venous lines as appropriate to the phase of the machine. The occlusion of the tubes may be achieved by means of a single clamp (as disclosed in U.S. Pat. No. 4,061,142) or by two separate clamps--an arterial line clamp and a venous line clamp. The clamp on the arterial line is normally open; that is, when power is withheld from the clamp, the tubing is open. For safety reasons however, the venous line clamp must be occluded when the clamp is not receiving power (hence the venous line clamp may also be referred to as the "safety clamp").
In the usual course of operation, a microprocessor within the hemodialysis machine regulates the cycling of blood flow and controls the opening and closing of the arterial and venous line clamps. Typical clamping devices used to occlude the flexible tubing make use of a solenoid and lifting magnets which are connected to a clamping mechanism. These clamps typically require large amounts of power, leading to the generation of significant amounts of heat during operation. These solenoid clamps have been known to fail because of elevated temperatures during operating conditions. Furthermore, conventional solenoid clamps also generate considerable noise during operation, providing, in addition to the dialysis itself, an additional irritation to the patient. A further disadvantage of conventional solenoid-based clamps is that these clamps respond relatively slowly to signals received from the hemodialysis machine microprocessor. Delays in opening or closing the clamps can result in admixing of treated and untreated blood.
It is therefore an object of this invention to provide a clamp suitable for occluding flexible tubes, which operates on relatively low power and generates less heat.
It is a further object of this invention to provide a clamp suitable for occluding flexible tubes wherein the clamp responds rapidly to a received signal.
It is also an object of this invention to provide a clamp suitable for occluding flexible tubes in a single needle dialysis apparatus and similar applications, which generates less noise and attendant irritation to the patient.
These and other objects and advantages of the present invention will be more fully apparent from the following description and drawings referred to therein.